The field of the invention is metering and dispensing devices for a powder or granular material. More particularly, it relates to a powder dispensing closure which is connected to a container and can dispense accurate amounts of the powder into a liquid or container.
Dispensers of the type concerned with in this invention are disclosed in U.S. Pat. No. 4,032,050 and No. 5,469,992. Both of these dispensers disclose a rotatable metering disk (80 and 20, respectively) for materials to be dispensed. There are problems with a rotatable measuring piece and stationary feed pieces. These cannot effect a desired internal stirring action of the container contents. Without this action, a significant amount of powder can be left in the container and not deposited into the measuring chamber.
The prior art does not provide a metering and dispensing closure which is connectable to a container and affords suitable sealing for powder materials which are hygroscopic.
Currently, the only reliable and cost effective method for dispensing powdered chemicals from small containers (between 1 and 4 kg), is to use a water spray and screen approach. There are two important limitations with these systems; the feed-rate is very inconsistent, and the powder formulations are limited. Such a method is described in U.S. Pat. No. 5,007,559.
The feed-rate varies over at least a 3:1 range and sometimes more due to the amount of powder remaining in the container, any bridging that may occur due to solidification near the screen, water pressure, spray pattern variation, water temperature and batch to batch variations. To control the amount of product dispensed, these systems typically require a concentration feedback control sub-system to compensate for their variable feed-rates. By far the most common is the conductivity feedback control used in dishwashing applications. Stated another way, because of the feed-rate variation, “spray/screen” powder dispensing systems normally can not be used in applications where a repeatable dose is required. This invention avoids this limitation by providing a precise and consistent metered dose based on a volumetric measurement.
The “spray/screen” dispensers work only with a limited range of powders and formulations. Detergents, the most commonly fed powders, are limited to formulations that will not create excess exothermic heat if the spray should penetrate into the powder. This has typically meant that the caustic (typically NAOH or KOH) level needs to be kept below about 40% to prevent the possibility of steam generation within the container which can be a safety issue. The metering and dispensing closure of this invention would remove this limitation and allow more powerful detergent powders to be formulated with perhaps up to 70% caustic concentrations for soft-water dishwasher applications. This would represent a 40% to 50% increase in “power” in a single container.
Many powders simply cannot be fed at all using the “spray/screen” method. These include any powders that tend to absorb water quickly and turn into a gel before they can be dissolved at the screen. The metering and dispensing closure of this invention obviates this.